To translate power from an engine of a walk-behind (self-propelled) lawn mower to a drive wheel to propel the lawn mower, a slipping belt transmission system can be employed. In the slipping belt transmission system, a transmission operably engages and pivots about a drive axle shaft, which engages a drive wheel to affect a driving rotation thereof. When the transmission tilts in a first direction toward the engine (i.e., in a forward direction when the drive axle shaft is adjacent to a rear axle) to a disengaged state position, a belt tension acting on a drive belt connecting the transmission and the engine is decreased to increase belt slip and place the transmission in a disengaged state where power is not transmitted from the engine to drive the drive wheel via the drive axle shaft. When the transmission tilts, from the disengaged state position, in a second direction away from the engine (i.e., in a rearward direction when the drive axle shaft is adjacent to the rear axle) to an engaged state position, the belt tension acting on the drive belt connecting the transmission and the engine is increased to decrease belt slip and place the transmission in an engaged state where power is transmitted from the engine to drive the drive wheel via the drive axle shaft. The engaged state position can be a tilt position at which the transmission is level, i.e., not tilted.
The transmission is biased, e.g., via a return spring secured to a frame of the lawn mower, to tilt in the first direction to be in the disengaged state position. As such, when the lawn mower engine is started, the lawn mower may not driven by the drive wheel until some control is made to counteract the biasing of the transmission to tilt in the first direction. This control can be carried out by actuating a clutch cable which pulls the transmission to tilt in the second direction to the engaged state position. The clutch cable can be secured to the transmission and connected to a mechanical operation lever on an operation handle of the lawn mower, which can be actuated by a user during lawn mower operation.
This slipping belt transmission system allows the user to control power supply to the drive wheel to propel the lawn mower. However, it does not allow for the drive speed of the lawn mower to be accurately controlled using the operation lever, particularly on relatively smooth surfaces with low rolling resistance.